In a heavy duty tire whose tread portion is provided with two shoulder regions respectively defined as being axially outside two shoulder main grooves and a crown region defined between the two shoulder regions, so called tread center wear where the crown region wears more than the other regions is liable to occur when the tire is mounted on a drive axle of a heavy duty vehicle such as truck and bus.
This is because the drive power of the heavy duty vehicle is especially large, and the contour of the tread portion of the tire is convexly curved such that the diameter of the tire becomes larger in the crown region than in the shoulder regions, and the crown region is subjected to the drive power more than the shoulder regions.
Heretofore, in order to reduce such tread center wear, the rigidity of the tread portion is increased in the crown region by increasing the ground contacting area of the ground contacting elements such as blocks and/or ribs formed in the crown region.
However, if the ground contacting area is increased in the crown region, widths of grooves formed in the crown region are decreased and wet performance is deteriorated.
Japanese Patent Application Publication No. H08-282213 discloses a heavy duly tire, wherein, in order to increase the uneven wear resistance, the axial distance from the tire equator to the widthwise center line of each shoulder circumferential groove is set in a rage from 0.25 to 0.40 times the tread width, and the crown region is divided into blocks by narrow axial grooves and narrow circumferential grooves.
Even in such tire, however, results which can completely satisfy both the tread center wear and the wet performance are not yet obtained.